This invention relates to the removal of ground water from deep wells for municipalities, industrial plants, and other users of ground water from wells.
Present practice is to drill a hole down to the water-bearing sand formation, and to install a permanent upper casing for the well. Then, through an underreaming process, a larger space is carved out from the sand formation, below the upper casing. A tubular screen of proper diameter is then installed, connected to the bottom of the casing, centered in the underreamed space, and gravel of properly selected size is filled into the underreamed space to form a gravel wall or filter around the outside of the screen inlet portion of the casing.
A vertical turbine pump is then installed at the top of the casing which serves as a discharge pipe. When the pump is put into operation, the water in the sand formation is drawn through the gravel and through the screen into the discharge pipe, from which it is elevated by the pump for use. The screen retains the gravel, and the gravel wall retains the sands in the water bearing formation from passing into the well casing.
A major problem encountered with these types of large water wells is that some sand particles do eventually pass through the gravel to the screen inlet portion of the well casing. Over time, sand particles begin to cake up and clog the holes or louvers in the screen. Also, over time, depending upon conditions, lime contained in the water will accumulate around the screen and will also plug up the holes and louvers in the screen. As the sand and lime builds or cakes up, it closes off portions of the screen. This naturally reduces pumping efficiency, reduces intake of water, increases the pumping head, and increases the pumping cost.
When the water level falls off to a point near the top portion of the screen portion of the casing, and the flow rate decreases, it becomes necessary to perform an operation known as air agitation within the screen to break up and remove the clogged sand and lime, to thereby clean and open up the screen for increasing intake of water and pumping efficiency. It is necessary to perform the air agitation cleaning operation every 2 or 3 years in large municipal or industrial water wells.
Present air agitation and cleaning practice involves the steps of removing the pump with a crane, lowering a string of agitating pipe having a scrubbing or cleaning device at the lower end thereof for scrubbing the inside of the screen. An air pipe is inserted within the agitating pipe. Air under pressure is introduced through the air pipe into the agitating pipe and, concurrently, the agitating pipe is moved up and down causing the scrubbing device to scrape the inside of the screen. This motion and the air cooperates to cause a suction pressure which breaks up the sand and lime formations plugging the screen and causes the particles on the outside thereof to pass through the screen into the well casing. The air lifts the water inside the well casing up through the agitating pipe to thereby remove the sand and lime particles in the water from the well.
An important step in the air agitation cleaning operation is the scrubbing process. Typically, the agitation pipe with attached scrubbing and scraping device is alternately moved up and down with a two foot stroke. Power driven mean are provided to move the agitation pipe up and down inside the well casing to create the scrubbing action.
Under conventional practice, once the pump is pulled out of the well, the crane is moved off the site and a large cable tool or drilling rig is transported to the site. The rig utilizes a motor drive gear having an eccentric connection to a cable. The cable is connected to the top of the agitating cleaner unit or assembly, and the motor driven gear and cable alternately lifts the assembly a distance of two feet (or whatever length of stroke is desired), after which the assembly decends by gravity within the well casing a distance of two feet. The gear then lifts the cleaner assembly again to create the reciprocating movement of the scraping device at the end of the agitating pipe.
After a screen portion of the casing is scrubbed for a predetermined period of time, the unit is lowered two feet into the well casing, and the scrubbing action is repeated. This process is continued until the entire screen portion has been scrubbed, at all times using the pressurized air in combination with the scraping device to agitate the well and thereby break up or dislodge the caked sand and lime clogging the screen.
When the air agitation process is completed, the rig is removed from the site. The crane is then brought back to the site to pull the agitation pipe out of the well and to remount the pump over the well so that normal pumping may resume.
The above-described practice using a crane to remove the pump and to insert the agitating pipe into the well, then transporting the cable tool rig to the site to perform the cleaning function, and then removing the cable tool rig from the site and returning the crane to the site to pull the agitating pipe out of the well casing and to remount the pump, is extremely time consuming and costly.